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In all tests conducted by US institutions, Hu-Friedy scalers and hemostats and A-Dec evacuation tips were contaminated with microorganisms and blood. In some cases, hydroxyapatite was added to the contamination to simulate tooth material.
The microbial challenge was determined prior to disinfection. Each instrument was inoculated with up to 500,000,000 microorganisms, usually by submerging the instruments completely in the contaminated soil. Up to 12 instruments constituted a test load, i.e. 6,000,000,000 microorganisms in the wash chamber. To prove the effectiveness of the machine when fully loaded, the chamber was then filled up with inocluated instruments. In most cases, no microorganisms could be recultured, indicating that usually each and every microorganism was killed.
To consider the worst case scenario, these tests were conducted in two series: One series in which the instruments were processed in the G 7881 Dental Washer Disinfector immediately after inoculation. In the second test series, the instruments were dried for six hours after inoculation with organisms and blood, but before processing.
To further increase the challenge, part of the instruments were scratched both with a rotating metal brush and with a grinding stone. The resulting fine and deep scratches on the surface of the instruments are hard to clean and disinfect, and may provide a safe harbor for microorganisms. Nonetheless, scratched instruments are commonly used in practice.
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